1. Field of the Invention
The present invention relates to a heat exchanger, a light source apparatus, and a projector, specifically to a technology of a heat exchanger suitable for a light source apparatus of a projector.
2. Description of the Related Art
A solid-state light source, specifically a light-emitting diode element which is referred to as “LED” hereinbelow is expected to be used for a light source apparatus of a compact projector because of its characteristics such as compact size, capability of instant blinking and lighting, high color purity, long life, and the like. Since most electrical current fed to the LED is converted to heat, the LED with higher intensity causes deterioration in light-emission efficiency due to an increase in calorific power. Therefore, it is desired to enhance a heat-radiation efficiency to improve the light-emission efficiency of the LED. Since the known air system using a fan is not sufficient enough to enhance the heat-radiation efficiency of the LED, a technology in which the LED is cooled by making a refrigerant flow has been proposed. Since the LED has high heating density, it is desirable to make the refrigerant flow at as close position to a heat source as possible. Furthermore, a configuration of making the refrigerant flow through multiple fine channels, each of which is several micrometers to several hundred micrometers in width, enables an increase in the contact area between the refrigerant and the channel wall, resulting in an efficient heat exchange. Typically, the fine channel can be formed by etching or wire-electric-discharge machining. However, since the etching or wire-electric-discharge machining requires high cost as well as long time, it is desirable that the fine channel is formed in any easier machining from the standpoint of mass-producing the heat exchanger. JP-A-2005-85887, for example, proposes a technology for forming a plurality of fine channels in an easy machining at low cost.
JP-A-2005-85887 discloses a configuration of a cooling plate in which a corrugated fin as a corrugated plate member is surrounded by an incrustation plate. The incrustation plate is formed by jointing two shaped plates. For an efficient heat exchange, it is desirable that a particular portion, which is in contact with the heat source, of the incrustation plate is formed to be as flat as possible to enable the heat source to closely contact the cooling plate. However, when the incrustation plate is formed by using a plate, it is difficult to realize the flatness since the center portion of the plate as the portion in contact with the heart source tends to warp. The warp of the incrustation plate requires additional process of forming the flatness of the portion in contact with the heat source, which increases man-hour necessary for manufacturing the heat exchanger. Moreover, forming of the incrustation plate requires shaping process for both of the two plates, which leads to a difficulty in reducing man-hour.
Besides, when there presents fluctuation in the distance between the incrustation plate and a fold of the corrugated fin on the heat source side, a clearance may arise between the fold and the incrustation plate. Since the efficiency of the heat exchange deteriorates if the contact between the fold and the incrustation plate is insufficient, such clearance is filled with a heat-conductive adhesive or a wax material. However since the thermal conductivity of the heat-conductive adhesive and the wax material is poorer than that of copper or aluminum forming the corrugated fin, thicker filling of the heat-conductive adhesive or the wax material degrades the performance of the heat exchanger. To eliminate the fluctuation in the distance between the incrustation plate and the fold of the corrugated fin, it is desirable to arrange the fold in line to have the same height at the stage of manufacturing the corrugated fin. Conventionally, a press work using a gear roll is employed for forming the corrugated fin, for example. In such a press work, it is very difficult to form the fold in line to have the same height with a high degree of accuracy. To realize high heat-exchange efficiency, it is desired to form as many fine channels as possible so that the contact area between a fluid and the channel wall increases. To form many fine channels for the compact heat source, it is necessary to form the corrugated fin whose corrugated pitch is made to be as small as possible. As a curve of the fold of the corrugated fin becomes smaller, the rigidity of the fold increases, and thereby it becomes difficult to implement an additional machining for arranging the fold in line to have the same height. For example, it is possible to improve the heat-exchange efficiency with a configuration that the fold is fixed to the incrustation plate to keep the distance of the corrugation. In this case, the manufacturing cost soars since it is necessary to implement a process for fixing the fold to the two members constituting the incrustation plate, and the corrugated fin may be deformed due to a compression force imposed by the two members to the corrugated fin. When the corrugated fin is deformed, the flow of the refrigerant becomes uneven due to the deformation of the fine channel, which leads to a difficulty in the efficient heat exchange.